Single-stroke radiation anti-scatter device for x-ray exposure window

Abstract

A radiation anti-scatter device comprising a grid and a grid driver connected to the grid for unidirectionaly moving the grid with a variable grid velocity along a path between a starting and an end position, and a method of providing such grid motion. The variable grid velocity may have a velocity profile V1=k1t for a first period and then V2=k2t-m for a second period, where V1 and V2 are velocity, k1 and k2 are constants, t is time, and m is an exponent having a value greater than 0. The anti-scatter device may be a component of a direct radiographic diagnostic imaging system which includes an image-producing element having an array of radiation detectors aligned in rows, and where the anti-scatter device is a grid having vanes oriented at an angle to the detector rows. Radiation emission may be synchronized with the grid motion to optimize a radiograph for a particular grid, radiation source, or examination procedure. The apparatus implements a method for reducing Moiré patterns in radiographic detectors having an array of sensors by unidirectionaly moving the grid in a single stroke during the radiation exposure with an asymptotically decreasing speed profile such that grid motion is maintained for a plurality of different radiation exposure times.

We claim:  
     
       1. A radiation anti-scatter device comprising: 
       a grid having a plurality of radiation absorbing elements,  
       a grid path comprising a start grid position at a first end of said path and a finish grid position at a second end of said path; and  
       a grid driver connected to said grid for moving said grid during an operating cycle from said start position to said finish grid position in a single unidirectional stroke at a variable speed along said path.  
     
     
       2. The radiation anti-scatter device according to claim  1 , wherein said variable speed comprises a velocity profile having a decreasing velocity component. 
     
     
       3. The radiation anti-scatter device according to claim  2 , wherein said velocity profile also comprises an increasing velocity component. 
     
     
       4. The radiation anti-scatter device according to claim  2  wherein the velocity profile comprises V=K 2 t −m , where V is the grid velocity, K 2  is a constant, t is time and m is an exponent having a value greater than 0. 
     
     
       5. A radiation anti-scatter device comprising: 
       a grid having a plurality of radiation absorbing elements, and a grid driver connected to said grid for moving said grid in a single unidirectional stroke at a variable speed between a starting and an end position, wherein said variable speed comprises a velocity profile and wherein the velocity profile comprises a first velocity component V 1 =K 1 t for a first period and a second velocity component V 2 =K 2 t −m  for a second period, where K 1  and K 2  are constants and m is greater than zero and equal to or less than one.  
     
     
       6. A direct radiographic diagnostic imaging system comprising: 
       a source of penetrative radiation for emitting on command a radiation beam along a path;  
       a radiation detector positioned in the beam path for receiving said radiation, said detector comprising an array of radiation sensors aligned in a first direction; and  
       a movable radiation anti-scatter grid assembly positioned between said radiation source and said detector, said grid assembly comprising:  
       a grid having a plurality of radiation absorbing elements oriented in a second direction at an angle to said first direction, and  
       a grid driver adapted to traverse said grid in a single stroke across the detector with a variable speed profile.  
     
     
       7. The system of claim  6  wherein said angle is 90 degrees. 
     
     
       8. The system of claim  7  wherein said grid traverses said detector in the first direction. 
     
     
       9. The system of claim  6  wherein said angle is an acute angle. 
     
     
       10. The system of claim  9  wherein said grid traverses said detector in a direction substantially perpendicular to said second direction. 
     
     
       11. The system of claim  6  wherein said velocity profile comprises V 1 =K 1 t for a first period and then V 2 =K 2 t −m  for a second period, where V 1  and V 2  are velocity, K 1  and K 2  are constants, t is time, and m is an exponent having a value greater than 0. 
     
     
       12. The system of claim  8  further comprising a controller adapted to synchronize emission of said radiation beam with movement of said grid. 
     
     
       13. A method for reducing Moir{acute over (e)} patterns in a radiation detection system comprising a detector having an array of discreet sensors aligned along a first direction, a radiation exposure source, and an anti-scatter grid assembly located between said detector and said source, said method comprising traversing said grid across said detector once in a single unidirectional stroke with a variable velocity profile. 
     
     
       14. The method according to claim  13  wherein said velocity profile decreases asymptotically to zero. 
     
     
       15. A method for reducing Moir{acute over (e)} patterns in a radiation detection system comprising a detector having an array of discreet sensors aligned along a first direction, a radiation exposure source, and an anti-scatter grid assembly located between said detector and said source, said method comprising traversing said grid across said detector once in a single unidirectional stroke wherein the step of traversing said grid comprises: 
       A. first accelerating said grid to a first velocity;  
       B. beginning asymptotically decelerating said grid from said first velocity toward a final velocity; and  
       C. causing said radiation exposure source to emit radiation only after the onset of step “B”.  
     
     
       16. The method according to claim  15  wherein said accelerating step comprises accelerating the grid at a velocity profile V 1 =K 1 t decelerating the grid at a velocity profile V 2 =K 2 t −m , where K 1  and K 2  are constants and m is greater than zero. 
     
     
       17. The method according to claim  16  wherein the accelerating step has a duration t 1  of between about 0.001 and 0.5 seconds and the decelerating step has a duration t 2  less than or equal to 2 seconds.